1. Field of the Invention
The present invention relates to a connecting structure for a bus bar and an electrical wire, and more particularly to a connecting structure for a bus bar and an electrical wire, for use in a power supply device mounted on an electric vehicle or a hybrid vehicle.
2. Description of the Related Art
An electric vehicle using an electric motor to travel or a hybrid vehicle using an electric motor in combination with an engine to travel needs a power supply device which supplies a high voltage and a high output to the electric motor, in order to travel smoothly. As the power supply device, a power supply device having a structure in which plural battery cells are connected in series is used.
Patent Literature 1 (Japanese Unexamined Patent Application Publication No. 2003-45409) discloses such a power supply device. The power supply device includes a battery module and a bus bar module. In the battery module, a battery cell is provided at one end with a positive electrode and at the other end with a negative electrode, and plural battery cells are arranged side by side under a condition where the positive electrode of one of adjacent battery cells is connected to the negative electrode of the other of the adjacent battery cells. The bus bar module contains plural bus bars which provide connections between the adjacent battery cells of the battery module and between the battery cells and an external device.
The plural battery cells are connected in series in such a manner that the positive electrode of one of the adjacent battery cells and the negative electrode of the other battery cell pass through the bus bar. An end of an electrical wire (voltage detection wire) is connected to the bus bar thereby to measure a potential of each battery cell or a voltage of the battery module. Patent Literature 1 discloses a structure in which the bus bar and a voltage detection terminal to which a core wire on the end of the electrical wire has been clamped and connected, are fastened together thereby to provide an electrical connection between the bus bar and the voltage detection terminal.
Patent Literatures 2 (Japanese Unexamined Patent Application Publication No. 2011-40332) and 3 (Japanese Unexamined Patent Application Publication No. 2012-59658) each disclose a conventional structure for connection between the bus bar and the electrical wire such as the voltage detection wire.
In the connecting structure disclosed in Patent Literature 2, the bus bar is welded to the core wire on the end of the electrical wire thereby to provide an electrical connection between the bus bar and the electrical wire. This eliminates the need for a process for connecting the voltage detection terminal to the end of the electrical wire and a process for fastening the bus bar and the voltage detection terminal together.
In the connecting structure disclosed in Patent Literature 3, a crimp terminal separate from the bus bar is used to crimp the electrical wire and the bus bar together thereby to provide an electrical connection between the bus bar and the electrical wire.
In the connecting structure disclosed in Patent Literature 2, the core wire on the end of the electrical wire is merely welded to the bus bar, and thus, if the electrical wire vibrates due to vibrations or the like, stress acts directly on a welded portion. Therefore, this structure has the problem of impairing reliability of connection. A clamping portion for a coating portion of the electrical wire linked to the welded portion may be set in order to solve the problem. In this case, however, a process for welding the core wire and a process for clamping the coating portion of the electrical wire are necessary, thus leading to a complicated connection operation.
In the connecting structure disclosed in Patent Literature 3, the crimp terminal is used to crimp the electrical wire and the bus bar together, and thus, the vibrations of the electrical wire has little direct influence. However, if the bus bar or the core wire of the electrical wire is made of an aluminum material, an oxide film develops on the surface of the bus bar or the core wire. The oxide film increases contact resistance on a crimp surface of the bus bar and the electrical wire, thus leading to the problem of causing heat generation or the like.